1. Field of the Invention
The current invention relates to cooling or warming of the body of a patient, or selective cooling or warming of a selected organ, by cooling or warming the blood in a major artery, or cooling or warming the blood flowing into the selected organ. This thermal treatment can protect the tissue from injury caused by anoxia or trauma, or it can achieve other purposes.
2. Background Information
Organs of the human body, such as the brain, kidney, and heart, are maintained at a constant temperature of approximately 37° C. Cooling of organs below 35° C. is known to provide cellular protection from anoxic damage caused by a disruption of blood supply, or by trauma. Cooling can also reduce swelling associated with these injuries.
Hypothermia is currently utilized in medicine and is sometimes performed to protect the brain from injury. Cooling of the brain is generally accomplished through whole body cooling to create a condition of total body hypothermia in the range of 20° to 30° C. This cooling is accomplished by immersing the patient in ice, by using cooling blankets, or by cooling the blood flowing externally through a cardiopulmonary bypass machine.
Some physicians have immersed the patient's head in ice to provide brain cooling. There are also cooling helmets, or head gear, to perform the same. This approach suffers from the problems of slow cool down and poor temperature control due to the temperature gradient that must be established externally to internally. It has also been shown that complications sometimes associated with total body cooling, such as arrhythmia and decreased cardiac output, can also be caused by cooling of the face and head only.
Selective organ hypothermia has also been attempted by perfusing the organ with a cold solution, such as saline or perflourocarbons. This is commonly done to protect the heart during heart surgery and is referred to as cardioplegia. This procedure has a number of drawbacks, including limited time of administration due to excessive volume accumulation, cost and inconvenience of maintaining the perfusate, and lack of effectiveness due to temperature dilution from the blood. Temperature dilution by the blood is a particular problem in high blood flow organs such as the brain. For cardioplegia, the blood flow to the heart is minimized, and therefore this effect is minimized.
Intravascular hypothermia, created by cooling the blood flowing in a selected artery, avoids many of the aforementioned complications. First, because the blood is cooled intravascularly, or in situ, problems associated with external circulation of blood are eliminated. Second, only a single puncture and arterial vessel cannulation is required, and it can be performed at an easily accessible artery such as the femoral, subclavian, or brachial. Third, cold perfusate solutions are not required, thus eliminating problems with excessive fluid accumulation. This also eliminates the time, cost, and handling issues associated with providing and maintaining cold perfusate solution. Fourth, rapid cooling can be achieved. Fifth, precise temperature control is possible.
One important factor related to catheter development for hypothermia is the small size of the artery in which the catheter may be placed, and the need to prevent a significant reduction in blood flow when the catheter is placed in the artery. A significant reduction in blood flow would result in ischemic organ damage. This situation is exacerbated if, for instance, cooling of the blood in an artery results in the constriction of the artery in the area where cooling is applied.